The garden fountain must have eaten too little of the prescribed fiber and suffers from constipation now. The laxative I tried first was an enema, of no avail. The second approach was of chemical nature: a saturated solution of 2-hydroxypropane-1,2,3-tricarboxylic acid in water at a temperature of about 360K, filled in and let it sit over night. That was unnecessary long, groundwater flows, too, I know, but it was the easiest way.
It helped, but not much. I’ll try it one more time next week but I have my doubts.